“The same Latin word — locusta — meant both 'locust' and 'lobster.' Romans apparently saw the same animal in two very different creatures.”
Latin locusta had two meanings: a swarming grasshopper and a lobster. The shared word probably reflects a visual resemblance — both have segmented bodies, jointed legs, and an exoskeleton. Pliny the Elder used the same word for both without clarification, relying on context. English eventually split the meanings: locust came through Old French locuste for the insect, while lobster came through Old English loppestre, a corruption of the same Latin root. The two English words are siblings that no longer recognize each other.
Locust swarms are among the most destructive natural events on earth. A single desert locust swarm can contain 80 million insects per square kilometer and travel 150 kilometers in a day. In 2020, East Africa experienced its worst locust invasion in seventy years — swarms covering 2,400 square kilometers destroyed crops across Kenya, Ethiopia, and Somalia. The Book of Exodus made locusts the eighth plague. Three thousand years later, the description is still accurate.
The transformation from solitary grasshopper to swarming locust is triggered by crowding. When desert locusts (Schistocerca gregaria) are forced into close contact — usually by rain concentrating vegetation — their bodies release serotonin, which changes their color, behavior, and even body shape. The solitary phase is green and shy. The gregarious phase is yellow-black, aggressive, and ravenous. They are the same species. The same insect can be a harmless grasshopper or a biblical plague, depending on how many neighbors it has.
The word locust has been misapplied to periodical cicadas in North America since at least the seventeenth century. Early colonists called them 'seventeen-year locusts,' and the name stuck despite cicadas and locusts being unrelated. True locusts are grasshoppers. Cicadas are closer to aphids. The confusion persists because both emerge in overwhelming numbers, and English speakers have always reached for the most dramatic word available.
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Desert locust swarms still threaten food security for roughly one-tenth of the world's population, primarily in Africa and the Middle East. The FAO maintains a global locust monitoring network. Satellite tracking, drone surveillance, and targeted pesticide application have improved response times, but no one has figured out how to prevent the swarming phase from triggering in the first place.
The serotonin switch that turns a solitary grasshopper into a swarming locust is one of the most dramatic behavioral transformations in biology. The word locust names not a species but a state — a grasshopper that has crossed a threshold into collective destruction. The Romans saw the same animal in a lobster. They were not entirely wrong.
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